Light emitting device, method of manufacturing the same, and display device

ABSTRACT

A light emitting device including a first electrode, a second electrode, a quantum dot layer disposed between the first electrode and the second electrode and a first auxiliary layer disposed between the quantum dot layer and the first electrode, wherein the first auxiliary layer includes nickel oxide nanoparticles having an average particle diameter of less than or equal to about 10 nanometers (nm) and an organic ligand, a method of manufacturing the light emitting device, and a display device including the same.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2019-0116948 filed in the Korean IntellectualProperty Office on Sep. 23, 2019, and all the benefits accruingtherefrom under 35 U.S.C. § 119, the content of which in its entirety isherein incorporated by reference.

BACKGROUND 1. Field

A light emitting device, a method of manufacturing the light emittingdevice, and a display device including the light emitting device aredisclosed.

2. Description of the Related Art

Physical characteristics (e.g., bandgap energies and melting points) ofnanoparticles that are intrinsic characteristics may be controlled bychanging the particle size of the nanoparticles, unlike bulk materials.For example, semiconductor nanocrystals also known as quantum dots maybe supplied with photoenergy or electrical energy and may emit light ina wavelength corresponding to sizes of the quantum dots. Accordingly,quantum dots may be used as a light emitting element emitting light of aparticular wavelength.

SUMMARY

A quantum dot device may use quantum dots as a light emitting body. Amethod of improving performance of the light emitting device usingquantum dots as a light emitting body is desired.

An embodiment provides a light emitting device capable of realizingimproved performance.

An embodiment provides a method of manufacturing the light emittingdevice.

An embodiment provides a display device including the light emittingdevice.

According to an embodiment, a light emitting device includes a firstelectrode, a second electrode, a quantum dot layer disposed between thefirst electrode and the second electrode, and a first auxiliary layerdisposed between the quantum dot layer and the first electrode, whereinthe first auxiliary layer includes nickel oxide nanoparticles having anaverage particle diameter of less than or equal to about 10 nanometers(nm) and an organic ligand.

The average particle diameter of the nickel oxide nanoparticles may beless than about 5 nm.

About 90% or greater of a total number of the nickel oxide nanoparticlesin the first auxiliary layer may have a particle size within ±about 30%of the average particle diameter of the nickel oxide nanoparticles.

The nickel oxide nanoparticles may include a metal dopant other thannickel.

The metal dopant may include copper, aluminum, molybdenum, vanadium,iron, lithium, manganese, silver, cobalt, zirconium, chromium, zinc, ora combination thereof.

The metal dopant may be present in an amount of less than or equal toabout 20 weight percent (wt %), based on a total weight of the nickeloxide nanoparticles.

The organic ligand may be derived from a substituted or unsubstituted C1to C10 alkylamine compound, a substituted or unsubstituted C2 to C10carboxylic acid compound, or a combination thereof.

The organic ligand may be derived from a substituted or unsubstitutedpentylamine, a substituted or unsubstituted hexylamine, a substituted orunsubstituted heptylamine, a substituted or unsubstituted octylamine, asubstituted or unsubstituted nonylamine, a substituted or unsubstitutedpentanoic acid, a substituted or unsubstituted hexanoic acid, asubstituted or unsubstituted heptanoic acid, a substituted orunsubstituted octanoic acid, a substituted or unsubstituted nonanoicacid, or a combination thereof.

The organic ligand may be present in an amount of less than or equal toabout 30 wt %, based on a total weight of the first auxiliary layer.

The light emitting device may further include a second auxiliary layerdisposed between the first auxiliary layer and the quantum dot layer.

The second auxiliary layer may includepoly(9,9-dioctyl-fluorene-co-N-(4-butylphenyl)-diphenylamine (TFB),polyarylamine, poly(N-vinylcarbazole), poly(3,4-ethylenedioxythiophene)(PEDOT), poly(3,4-ethylenedioxythiophene) polystyrene sulfonate(PEDOT:PSS), polyaniline, polypyrrole, N,N,N′,N′-tetrakis(4-methoxyphenyl)-benzidine (TPD),4-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl (alpha-NPD), m-MTDATA(4,4′,4″-tris[phenyl(m-tolyl)amino]triphenylamine),4,4′,4″-tris(N-carbazolyl)-triphenylamine (TCTA),1,1-bis[(di-4-tolylamino)phenylcyclohexane (TAPC), a p-type metal oxide,graphene oxide, or a combination thereof.

The light emitting device may further include a third auxiliary layerdisposed between the quantum dot layer and the second electrode and thethird auxiliary layer may include zinc oxide nanoparticles representedby Zn_(1-x)M_(x)O (wherein M is Mg, Ca, Zr, W, Li, Ti, or a combinationthereof and 0≤x<0.5).

The light emitting device may include an anode and a cathode, a lightemitting layer including a non-cadmium-based quantum dot disposedbetween the anode and the cathode, and a hole auxiliary layer disposedbetween the anode and the light emitting layer, the hole auxiliary layerincluding nickel oxide nanoparticles.

According to an embodiment, a method of manufacturing a light emittingdevice includes providing a first electrode, forming a first auxiliarylayer including nickel oxide nanoparticles having an average particlediameter of less than or equal to about 10 nm and an organic ligand onthe first electrode, forming a quantum dot layer on the first auxiliarylayer, and forming a second electrode on the quantum dot layer tomanufacture the light emitting device.

The forming of the first auxiliary layer may be performed by a solutionprocess.

The forming of the first auxiliary layer may include obtaining thenickel oxide nanoparticles and the organic ligand from a precursormixture including a nickel oxide precursor and an organic ligandprecursor, obtaining a composition for a first auxiliary layer includingthe nickel oxide nanoparticles and the organic ligand, and coating thecomposition for the first auxiliary layer to form the first auxiliarylayer.

The organic ligand precursor may include a substituted or unsubstitutedC1 to C10 alkylamine compound, a substituted or unsubstituted C2 to C10carboxylic acid compound, or a combination thereof.

The organic ligand precursor may include a substituted or unsubstitutedpentylamine, a substituted or unsubstituted hexylamine, a substituted orunsubstituted heptylamine, a substituted or unsubstituted octylamine, asubstituted or unsubstituted nonylamine, a substituted or unsubstitutedpentanoic acid, a substituted or unsubstituted hexanoic acid, asubstituted or unsubstituted heptanoic acid, a substituted orunsubstituted octanoic acid, a substituted or unsubstituted nonanoicacid, or a combination thereof.

The obtaining the nickel oxide nanoparticles and the organic ligand mayinclude heat treating the precursor mixture at a temperature of lessthan or equal to about 150° C.

The coating of the composition for the first auxiliary layer may includecoating the composition for the first auxiliary layer by a spin coating,a spray coating, a slit coating, a dip coating, an inkjet printing, anozzle printing, a doctor blade coating, or a combination thereof.

The coating of the composition for the first auxiliary layer may includeheat-treating at a temperature of less than 500° C.

According to an embodiment, a display device including the lightemitting device is provided.

The performance of the light emitting device may be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other advantages and features of this disclosure willbecome more apparent by describing in further detail exemplaryembodiments thereof with reference to the accompanying drawings, inwhich:

FIG. 1 is a schematic cross-sectional view of a light emitting deviceaccording to an embodiment,

FIG. 2 is a transmission electron microscopic (TEM) image showing themorphology of the thin film of Preparation Example 1,

FIG. 3 is a transmission electron microscopic (TEM) image showing themorphology of the thin film of Preparation Example 2,

FIG. 4 is a scanning electron microscopic (SEM) image showing themorphology of the thin film of Reference Preparation Example 1,

FIG. 5 is a scanning electron microscopic (SEM) image showing themorphology of the thin film of Reference Preparation Example 2,

FIG. 6 is a graph of weight (percent (%)) versus temperature (Temp) (°C.) of the thin film of Preparation Example 1, Preparation Example 4,and Reference Preparation Example 1,

FIG. 7 is a graph of luminance (%) versus hours showing life-spancharacteristics of the light emitting devices of Example 1 andComparative Example 1,

FIG. 8 is a graph of luminance (%) versus hours showing life-spancharacteristics of the light emitting devices of Example 2 to Example 4and Comparative Example 3, and

FIG. 9 is a graph of voltage (volts (V)) versus hours showing life-spancharacteristics of the light emitting devices of Example 2 to Example 4and Comparative Example 3.

DETAILED DESCRIPTION

Hereinafter, example embodiments of the present disclosure will bedescribed in detail so that a person skilled in the art would understandthe same. This disclosure may, however, be embodied in many differentforms and is not construed as limited to the example embodiments setforth herein.

In the drawings, the thickness of layers, films, panels, regions, etc.,are exaggerated for clarity. Like reference numerals designate likeelements throughout the specification. It will be understood that whenan element such as a layer, film, region, or substrate is referred to asbeing “on” another element, it can be directly on the other element orintervening elements may also be present. In contrast, when an elementis referred to as being “directly on” another element, there are nointervening elements present.

It will be understood that, although the terms “first,” “second,”“third” etc. may be used herein to describe various elements,components, regions, layers and/or sections, these elements, components,regions, layers and/or sections should not be limited by these terms.These terms are only used to distinguish one element, component, region,layer, or section from another element, component, region, layer, orsection. Thus, “a first element,” “component,” “region,” “layer” or“section” discussed below could be termed a second element, component,region, layer, or section without departing from the teachings herein.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein,“a”, “an,” “the,” and “at least one” do not denote a limitation ofquantity, and are intended to include both the singular and plural,unless the context clearly indicates otherwise. For example, “anelement” has the same meaning as “at least one element,” unless thecontext clearly indicates otherwise. “At least one” is not to beconstrued as limiting “a” or “an.” “Or” means “and/or.” As used herein,the term “and/or” includes any and all combinations of one or more ofthe associated listed items. It will be further understood that theterms “comprises” and/or “comprising,” or “includes” and/or “including”when used in this specification, specify the presence of statedfeatures, regions, integers, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, regions, integers, steps, operations, elements,components, and/or groups thereof.

“About” as used herein is inclusive of the stated value and means withinan acceptable range of deviation for the particular value as determinedby one of ordinary skill in the art, considering the measurement inquestion and the error associated with measurement of the particularquantity (i.e., the limitations of the measurement system). For example,“about” can mean within one or more standard deviations, or within ±10%or 5% of the stated value.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

Exemplary embodiments are described herein with reference to crosssection illustrations that are schematic illustrations of idealizedembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, embodiments described herein should not beconstrued as limited to the particular shapes of regions as illustratedherein but are to include deviations in shapes that result, for example,from manufacturing. For example, a region illustrated or described asflat may, typically, have rough and/or nonlinear features. Moreover,sharp angles that are illustrated may be rounded. Thus, the regionsillustrated in the figures are schematic in nature and their shapes arenot intended to illustrate the precise shape of a region and are notintended to limit the scope of the present claims.

As used herein, the term “Group” may refer to a group of Periodic Table.

As used herein, “Group I” may refer to Group IA and Group IB, andexamples may include Li, Na, K, Rb, and Cs, but are not limited thereto.

As used herein, “Group II” may refer to Group IIA and Group IIB, andexamples of Group metal may be Cd, Zn, Hg, and Mg, but are not limitedthereto.

As used herein, “Group III” may refer to Group IIIA and Group IIIB, andexamples of Group III metal may be Al, In, Ga, and TI, but are notlimited thereto.

As used herein, “Group IV” may refer to Group IVA and Group IVB, andexamples of a Group IV metal may be Si, Ge, and Sn, but are not limitedthereto. As used herein, the term “metal” may include a semi-metal suchas Si.

As used herein, “Group V” may refer to Group VA, and examples mayinclude nitrogen, phosphorus, arsenic, antimony, and bismuth, but arenot limited thereto.

As used herein, “Group VI” may refer to Group VIA, and examples mayinclude sulfur, selenium, and tellurium, but are not limited thereto.

As used herein, a work function, a highest occupied molecular orbital(HOMO) energy level, and a lowest unoccupied molecular orbital (LUMO)energy level are expressed as an absolute value from a vacuum level. Inaddition, when the work function, HOMO energy level, and LUMO energylevel are referred to be “deep,” “high” or “large,” the work function,HOMO energy level, and LUMO energy level have a large absolute valuebased on “electronvolts (eV)” of the vacuum level, while when the workfunction, HOMO energy level and LUMO energy level are referred to be“shallow,” “low,” or “small,” the work function, HOMO energy level, andLUMO energy level have a small absolute value based on “eV” of thevacuum level.

As used herein, when a definition is not otherwise provided,“substituted” refers to replacement of a hydrogen atom of a compound bya substituent of deuterium, a halogen atom (F, Br, Cl, or I), a hydroxygroup, a nitro group, a cyano group, an amino group, an azido group, anamidino group, a hydrazino group, a hydrazono group, a carbonyl group, acarbamyl group, a thiol group, an ester group, a carboxyl group or asalt thereof, a sulfonic acid group or a salt thereof, a phosphoric acidor a salt thereof, a C1 to C30 alkyl group, a C2 to C30 alkenyl group, aC2 to C30 alkynyl group, a C6 to C30 aryl group, a C7 to C30 arylalkylgroup, a C1 to C30 alkoxy group, a C1 to C20 heteroalkyl group, a C3 toC20 heteroarylalkyl group, a C3 to C30 cycloalkyl group, a C3 to C15cycloalkenyl group, a C6 to C15 cycloalkynyl group, a C2 to C30heterocyclic group, or a combination thereof.

In addition, two adjacent substituents of the substituted halogen atom(F, Br, Cl, or I), hydroxy group, nitro group, cyano group, amino group,azido group, amidino group, hydrazino group, hydrazono group, carbonylgroup, carbamyl group, thiol group, ester group, carboxyl group or saltthereof, sulfonic acid group or salt thereof, phosphoric acid group orsalt thereof, C1 to C30 alkyl group, C2 to C30 alkenyl group, C2 to C30alkynyl group, C6 to C30 aryl group, C7 to C30 arylalkyl group, C1 toC30 alkoxy group, C1 to C20 heteroalkyl group, C3 to C20 heteroarylalkylgroup, C3 to C30 cycloalkyl group, C3 to C15 cycloalkenyl group, C6 toC15 cycloalkynyl group, and C2 to C30 heterocyclic group may be fused toform a ring. For example, the substituted C6 to C30 aryl group may befused with another adjacent substituted C6 to C30 aryl group to form asubstituted or unsubstituted fluorene ring.

As used herein, when a definition is not otherwise provided, “hetero”refers to one including 1 to 3 heteroatoms of N, O, S, Se, or P.

As used herein, the particle diameter may be obtained by analyzing atwo-dimensional image obtained from an electron microscope analysis(e.g., TEM or SEM) with a commercially available image analysis program(e.g., image J).

As used herein, an average may be a mean, a mode, or a median.

As used herein, the average particle diameter may be a sum of a particlediameter of a plurality of particles divided by the number of particles.Hereinafter, a light emitting device according to an embodiment isdescribed with reference to drawings.

FIG. 1 is a schematic cross-sectional view of a light emitting deviceaccording to an embodiment.

Referring to FIG. 1, a light emitting device 10 according to anembodiment includes a first electrode 11 and a second electrode 16, aquantum dot layer 14 disposed between the first electrode 11 and thesecond electrode 16, a first auxiliary layer 12 disposed between thequantum dot layer 14 and the first electrode 11, a second auxiliarylayer 13 disposed between the first auxiliary layer 12 and the quantumdot layer 14, and a third auxiliary layer 15 disposed between thequantum dot layer 14 and the second electrode 16.

A substrate (not shown) may be disposed at the first electrode 11 sideor the second electrode 16 side. The substrate may be, for example, madeof an inorganic material such as glass; an organic material such aspolycarbonate, polymethylmethacrylate, polyethylene terephthalate,polyethylene naphthalate, polyamide, polyethersulfone, or a combinationthereof; or a silicon wafer. The substrate may be omitted.

One of the first electrode 11 and the second electrode 16 may be ananode and the other may be a cathode. For example, the first electrode11 may be an anode and the second electrode 16 may be a cathode. Forexample, the first electrode 11 may be a cathode and the secondelectrode 16 may be an anode. For example, the first electrode 11 andthe second electrode 16 may face each other.

The first electrode 11 may be for example made of a conductor, forexample a metal, a conductive metal oxide, or a combination thereof. Thefirst electrode 11 may include for example a metal or an alloy thereofsuch as nickel, platinum, vanadium, chromium, copper, zinc, and gold; aconductive metal oxide such as zinc oxide, indium oxide, tin oxide,indium tin oxide (ITO), indium zinc oxide (IZO), or fluorine doped tinoxide; or a combination of a metal and an oxide such as ZnO and Al orSnO₂ and Sb, but is not limited thereto. For example, the firstelectrode 11 may include a transparent conductive metal oxide, forexample, indium tin oxide. The first electrode 11 may have a higher workfunction than the work function of the second electrode 16 that will bedescribed later. The first electrode 11 may have a lower work functionthan the work function of the second electrode 16 that will be describedlater.

The second electrode 16 may be for example made of a conductor, forexample a metal, a conductive metal oxide, a conductive polymer, or acombination thereof. The second electrode 16 may include for example ametal or an alloy thereof such as aluminum, magnesium, calcium, sodium,potassium, titanium, indium, yttrium, lithium, gadolinium silver, gold,platinum, tin, lead, cesium, barium, and the like, a multi-layerstructure material such as LiF/Al, Li₂O/Al, Liq/Al, LiF/Ca, and BaF₂/Ca,but is not limited thereto. The conductive metal oxide is the same asdescribed herein.

For example, a work function of the first electrode 11 may be forexample about 4.5 eV to about 5.0 eV and a work function of the secondelectrode 16 may be for example greater than or equal to about 4.0 eVand less than about 4.5 eV. Within the disclosed ranges, the workfunction of the first electrode 11 may be for example about 4.6 eV toabout 4.9 eV and the work function of the second electrode 16 may be forexample about 4.0 eV to about 4.3 eV.

The first electrode 11, the second electrode 16, or a combinationthereof may be a light-transmitting electrode and the light-transmittingelectrode may be for example made of a conductive oxide such as a zincoxide, indium oxide, tin oxide, indium tin oxide (ITO), indium zincoxide (IZO), or fluorine doped tin oxide, or a metal thin layer of asingle layer or a multilayer. When one of the first electrode 11 and thesecond electrode 16 is a non-light-transmitting electrode, thenon-light-transmitting first electrode 11 or second electrode 16 may bemade of for example an opaque conductor such as aluminum (Al), silver(Ag), or gold (Au).

A thickness of the first electrode 11, a thickness of the secondelectrode 16, or a thickness of each of the first electrode 11 and thesecond electrode 16 are not particularly limited and may beappropriately selected taking into consideration device efficiency. Forexample, the thickness of the first electrode 11, the thickness of thesecond electrode 16, or the thickness of each of the first electrode 11and the second electrode 16 may be greater than or equal to about 5 nm,for example, greater than or equal to about 50 nm. For example, thethickness of the first electrode 11, the thickness of the secondelectrode 16, or the thickness of each of the first electrode 11 and thesecond electrode 16 may be less than or equal to about 100 micrometers(μm), for example, 10 μm, less than or equal to about 1 μm, less than orequal to about 900 nm, less than or equal to about 500 nm, or less thanor equal to about 100 nm.

The quantum dot layer 14 includes a quantum dot. The quantum dot may bea semiconductor nanocrystal, and may have various shapes, for example anisotropic semiconductor nanocrystal, a quantum rod, and a quantum plate.Herein, the quantum rod may indicate a quantum dot having an aspectratio of greater than about 1:1, for example an aspect ratio of greaterthan or equal to about 2:1, greater than or equal to about 3:1, orgreater than or equal to about 5:1. For example, the quantum rod mayhave an aspect ratio of less than or equal to about 50:1, of less thanor equal to about 30:1, or of less than or equal to about 20:1.

The quantum dot may have for example a particle diameter (a length ofthe largest portion for a non-spherical shape) of for example about 1 nmto about 100 nm, about 1 nm to about 80 nm, about 1 nm to about 50 nm,or about 1 nm to about 20 nm.

A bandgap energy of a quantum dot may be controlled according to sizesand a composition of the quantum dot, and photoluminescence wavelengthmay be controlled. For example, as the size of a quantum dots increases,the quantum dot may have a narrow energy bandgap energy and emit lightin a relatively long wavelength region while as the size of a quantumdots decreases, the quantum dot may have a wide bandgap energy and emitlight in a relatively short wavelength region.

For example, the quantum dot may emit for example light in apredetermined wavelength region of a visible region according to thesize, composition, or a combination thereof of the quantum dot. Forexample, the quantum dot may emit blue light, red light, or green light,and the blue light may have for example a peak emission wavelength inabout 430 nm to about 470 nm, the red light may have for example a peakemission wavelength in about 600 nm to about 650 nm, and the green lightmay have for example a peak emission wavelength in about 520 nm to about550 nm. For example, the quantum dot may emit blue light having a peakemission wavelength in a wavelength of about 430 nm to about 470 nm.

The quantum dot may have for example a quantum yield of greater than orequal to about 10%, greater than or equal to about 30%, greater than orequal to about 50%, greater than or equal to about 60%, greater than orequal to about 70%, or greater than or equal to about 90%.

The quantum dot may have a relatively narrow full width at half maximum(FWHM). Herein, the FWHM a width of a wavelength corresponding to a halfof a peak absorption point and as the FWHM is narrower, light in anarrower wavelength region may be emitted and high color purity may beobtained. The quantum dot may have for example a FWHM of less than orequal to about 50 nm, less than or equal to about 49 nm, less than orequal to about 48 nm, less than or equal to about 47 nm, less than orequal to about 46 nm, less than or equal to about 45 nm, less than orequal to about 44 nm, less than or equal to about 43 nm, less than orequal to about 42 nm, less than or equal to about 41 nm, less than orequal to about 40 nm, less than or equal to about 39 nm, less than orequal to about 38 nm, less than or equal to about 37 nm, less than orequal to about 36 nm, less than or equal to about 35 nm, less than orequal to about 34 nm, less than or equal to about 33 nm, less than orequal to about 32 nm, less than or equal to about 31 nm, less than orequal to about 30 nm, less than or equal to about 29 nm, or less than orequal to about 28 nm.

For example, the quantum dot may be for example a Group I-VIsemiconductor compound, a Group III-V semiconductor compound, a GroupIV-VI semiconductor compound, a Group IV semiconductor compound, a GroupI-III-VI semiconductor compound, a Group I-II-IV-VI semiconductorcompound, a Group II-III-V semiconductor compound, or a combinationthereof. The Group II-VI semiconductor compound may be for example abinary element compound such as CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnO, HgS,HgSe, HgTe, MgSe, MgS, or a combination thereof; a ternary elementcompound such as CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS,HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS,HgZnSe, HgZnTe, MgZnSe, MgZnS, or a combination thereof; a quaternaryelement compound such as HgZnTeS, CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS,CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, HgZnSTe, or a combination thereof;or a combination thereof, but is not limited thereto. The Group III-Vsemiconductor compound may be for example a binary element compound suchas GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, ora combination thereof; a ternary element compound such as GaNP, GaNAs,GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs,InNSb, InPAs, InPSb, GaAlNP, or a combination thereof; a quaternaryelement compound such as GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP,GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs,InAlPSb, or a combination thereof; or a combination thereof, but is notlimited thereto. The Group IV-VI semiconductor compound may be forexample a binary element compound such as SnS, SnSe, SnTe, PbS, PbSe,PbTe, or a combination thereof; a ternary element compound such asSnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, or acombination thereof; a quaternary element compound such as SnPbSSe,SnPbSeTe, SnPbSTe, or a combination thereof; or a combination thereof,but is not limited thereto. The Group IV semiconductor compound may befor example a singular element semiconductor compound such as Si, Ge, ora combination thereof; a binary element semiconductor compound of SiC,SiGe, or a combination thereof; or a combination thereof, but is notlimited thereto. The Group I-III-VI semiconductor compound may be forexample CunISe₂, CuInS₂, CuInGaSe, CuInGaS, or a combination thereof,but is not limited thereto. The Group I-II-IV-VI semiconductor compoundmay be for example CuZnSnSe, CuZnSnS, or a combination thereof, but isnot limited thereto. The Group II-III-V semiconductor compound mayinclude for example InZnP, but is not limited thereto.

The quantum dot may include the binary semiconductor compound, theternary semiconductor compound, or the quaternary semiconductor compoundin a substantially uniform concentration or partially differentconcentration distributions.

For example, the quantum dot may include a non-cadmium-based quantumdot. Cadmium (Cd) may cause environment/health problems and is arestricted element by Restriction of Hazardous Substances Directive(RoHS) in a plurality of countries, and it may be desirable to use anon-cadmium-based quantum dot. For example, in an embodiment, thequantum dot may not include cadmium, for example, the quantum dot maynot include cadmium, mercury, or lead.

For example, the quantum dot may include for example a Group III-Vsemiconductor compound including indium and phosphorus, and may furtherinclude for example zinc. For example, the quantum dot may include aGroup II-VI compound including a chalcogen element and zinc, and forexample the chalcogen element may be sulfur, selenium, tellurium, or acombination thereof.

For example, the quantum dot may be a semiconductor compound includingzinc (Zn) and tellurium (Te), selenium (Se), or a combination thereof.For example, the quantum dot may be a Zn—Te semiconductor compound, aZn—Se semiconductor compound, a Zn—Te—Se semiconductor compound, or acombination thereof. For example, in the Zn—Te—Se semiconductorcompound, an amount of tellurium (Te) may be less than that of selenium(Se). The semiconductor compound may have a peak emission wavelength ina wavelength region of less than or equal to about 470 nm, for examplein a wavelength region of about 430 nm to about 470 nm and may emit bluelight.

The quantum dot may have one quantum dot core and a multi-layeredquantum dot shell surrounding the core. Herein, the multi-layered shellhas at least two shells wherein each shell may be a single composition,may be an alloy, may have a concentration gradient, or a combinationthereof.

For example, a shell of a multi-layered shell that is farther from thecore may have a higher bandgap energy than a shell that is closer, e.g.,near, to the core, and the quantum dot may exhibit a quantum confinementeffect.

For example, the quantum dot having a core-shell structure may forexample include a core including InP, InZnP, ZnSe, ZnSeTe, or acombination thereof and a shell disposed on a, e.g., at least one,portion of the core and having a different composition from that of thecore. Herein, the shell may include InP, InZnP, ZnSe, ZnS, ZnSeTe,ZnSeS, or a combination thereof.

The quantum dot layer 14 may have for example a thickness of about 5 nmto about 200 nm, for example about 10 nm to about 150 nm, about 10 nm toabout 100 nm, or about 10 nm to about 50 nm.

The quantum dot layer 14 may have a relatively high HOMO energy leveland may be for example a HOMO energy level of greater than or equal toabout 5.4 eV, greater than or equal to about 5.6 eV, greater than orequal to about 5.7 eV, or greater than or equal to about 5.8 eV. TheHOMO energy level of the quantum dot layer 14 may be for example about5.4 eV to about 7.0 eV, about 5.4 eV to about 6.8 eV, about 5.4 eV toabout 6.7 eV, about 5.4 eV to about 6.5 eV, about 5.4 eV to about 6.3eV, about 5.4 eV to about 6.2 eV, or about 5.4 eV to about 6.1 eV,within the disclosed ranges, for example about 5.6 eV to about 7.0 eV,about 5.6 eV to about 6.8 eV, about 5.6 eV to about 6.7 eV, about 5.6 eVto about 6.5 eV, about 5.6 eV to about 6.3 eV, about 5.6 eV to about 6.2eV, or about 5.6 eV to about 6.1 eV, for example about 5.7 eV to about7.0 eV, about 5.7 eV to about 6.8 eV, about 5.7 eV to about 6.7 eV,about 5.7 eV to about 6.5 eV, about 5.7 eV to about 6.3 eV, about 5.7 eVto about 6.2 eV, or about 5.7 eV to about 6.1 eV.

The quantum dot layer 14 may have a relatively low LUMO energy level,and may have for example an LUMO energy level of less than or equal toabout 3.6 eV, for example less than or equal to about 3.5 eV, less thanor equal to about 3.4 eV, less than or equal to about 3.3 eV, less thanor equal to about 3.2 eV, or less than or equal to about 3.0 eV. TheLUMO energy level of the quantum dot layer 14 may be for example about2.5 eV to about 3.6 eV, about 2.5 eV to about 3.5 eV, about 2.5 eV toabout 3.4 eV, about 2.5 eV to about 3.3 eV, about 2.5 eV to about 3.2eV, about 2.5 eV to about 3.1 eV, or about 2.5 eV to about 3.0 eV.

The first auxiliary layer 12 may be disposed between the first electrode11 and the quantum dot layer 14 and may increase injection of chargesmoving from the first electrode 11 to the quantum dot layer 14, transfercharacteristics of charges moving from the first electrode 11 to thequantum dot layer 14, or a combination thereof or may block oppositecharges from flowing over from the quantum dot layer 14. The firstauxiliary layer 12 may be one layer or two or more layers. For example,the first auxiliary layer 12 may include a hole auxiliary layer toincrease injection of the holes moving from the first electrode 11 tothe quantum dot layer 14, movement characteristics of the holes movingfrom the first electrode 11 to the quantum dot layer 14, or acombination thereof; an electron blocking layer to block the chargesfrom flowing over from the quantum dot layer 14; or a combinationthereof. For example, the first auxiliary layer 12 may be a holeinjection layer to facilitate the injection of holes from the firstelectrode 11 or a hole transport layer to increase the transport ofholes from the first electrode 11 to the quantum dot layer 14.

The first auxiliary layer 12 may include an inorganic material, forexample an inorganic material as a main component. Herein the maincomponent may be included in an amount of greater than about 50 volumepercent (volume %), greater than or equal to about 55 volume %, greaterthan or equal to about 60 volume %, greater than or equal to about 70volume %, greater than or equal to about 80 volume %, greater than orequal to about 90 volume %, or greater than or equal to about 95 volume%, based on a total volume of the first auxiliary layer 12. Accordingly,stability against moisture, oxygen, etc. of the light emitting devicemay be improved, e.g., secured, interface resistance between the firstelectrode 11 and the first auxiliary layer 12 may be reduced bydecreasing or preventing corrosion of the first electrode 11 under thefirst auxiliary layer 12, and life-span of the emitting device may beimproved.

The first auxiliary layer 12 may include for example inorganicnanoparticles consisting of an inorganic material or including aninorganic material as a main component. The inorganic nanoparticles maybe two-dimensional or three-dimensional particles having a particlediameter of nanoscale, and may have for example a particle diameter lessthan or equal to about 20 nm, less than or equal to about 15 nm, lessthan or equal to about 10 nm, less than or equal to about 9 nm, lessthan or equal to about 8 nm, less than or equal to about 7 nm, less thanor equal to about 6 nm, or less than about 5 nm.

The average particle diameter of a plurality of inorganic nanoparticlesincluded in the first auxiliary layer 12 may be less than or equal toabout 10 nm for example, less than or equal to about 9 nm, less than orequal to about 8 nm, less than or equal to about 7 nm, less than orequal to about 6 nm, less than about 5 nm, less than or equal to about 4nm, less than or equal to about 3.5 nm, less than or equal to about 3.3nm or less than or equal to about 3.2 nm, for example greater than orequal to about 1 nm, for example, greater than or equal to about 2 nm,greater than or equal to about 2.3 nm, or greater than or equal to about2.5 nm.

Sizes of a plurality of inorganic nanoparticles included in the firstauxiliary layer 12 may be distributed relatively evenly. For example,about 90% or greater of the total number of the inorganic nanoparticlesincluded in the first auxiliary layer 12 may fall within about ±30%,about ±28%, about ±26%, about ±25%, about ±24%, about ±23%, or about±22% of the average particle diameter of the inorganic nanoparticles.Accordingly, the thickness of the first auxiliary layer 12 may beuniform.

For example, a standard deviation of a particle diameter of a pluralityof inorganic nanoparticles may be less than or equal to about 2 nm, lessthan or equal to about 1.7 nm, less than or equal to about 1.4 nm, lessthan or equal to about 1.2 nm, less than or equal to about 1 nm, lessthan or equal to about 0.8 nm, or less than or equal to about 0.5 nm.

For example, the inorganic nanoparticles may include metal oxidenanoparticles and may include for example p-type metal oxidenanoparticles. The p-type metal oxide nanoparticles may have arelatively high HOMO energy level to match an energy level of thequantum dot layer 14. For example, the p-type metal oxide nanoparticlesmay have a HOMO energy level that is the same as that of the quantum dotlayer 14 or less than a HOMO energy level of the quantum dot layer 14within a range of about 1.0 eV or less. For example, a differencebetween HOMO energy levels of the p-type metal oxide nanoparticles andthe quantum dot layer 14 may be about 0 eV to about 1.0 eV, for exampleabout 0.01 eV to about 0.8 eV, about 0.01 eV to about 0.7 eV, about 0.01eV to about 0.5 eV, about 0.01 eV to about 0.4 eV, about 0.01 eV toabout 0.3 eV, or about 0.01 eV to about 0.2 eV.

For example, the p-type metal oxide nanoparticles may have a HOMO energylevel of for example greater than or equal to about 5.0 eV, greater thanor equal to about 5.2 eV, greater than or equal to about 5.4 eV, orgreater than or equal to about 5.5 eV. For example, the p-type metaloxide nanoparticles may have a HOMO energy level of about 5.0 eV toabout 7.0 eV, for example about 5.2 eV to about 6.8 eV, about 5.4 eV toabout 6.8 eV, about 5.4 eV to about 6.7 eV, about 5.4 eV to about 6.5eV, about 5.4 eV to about 6.3 eV, about 5.4 eV to about 6.2 eV, or about5.4 eV to about 6.1 eV. Accordingly, the injection of holes from thefirst electrode, transport of holes from the first electrode, or acombination thereof may be facilitated to impart an excellent electricalcharacteristic to the light emitting device.

For example, the inorganic nanoparticles may include nickel-containingoxide nanoparticles (hereinafter, referred to as “nickel oxidenanoparticles”). The nickel oxide nanoparticles can have highcrystallinity, for example crystallinity of greater than or equal toabout 50%, greater than or equal to about 60%, greater than or equal toabout 70%, greater than or equal to about 80%, greater than or equal toabout 90%, greater than or equal to about 95%, or greater than or equalto about 98%. The nickel oxide nanoparticles may have for example acubic crystal structure (cubic system). For example, the nickel oxidenanoparticles may include a simple lattice structure, a body centerlattice structure, a face center lattice structure, or a combinationthereof. As the nickel oxide nanoparticles have crystallinity, chargeconductivity of the first auxiliary layer may be improved, and excellentelectrical characteristics may be provided to the light emitting device.

For example, the first auxiliary layer 12 may include a plurality ofnickel oxide nanoparticles. An average particle diameter of theplurality of nickel oxide nanoparticles may be for example less than orequal to about 10 nm, for example, less than or equal to about 9 nm,less than or equal to about 8 nm, less than or equal to about 7 nm, lessthan or equal to about 6 nm, less than about 5 nm, less than or equal toabout 4 nm, less than or equal to about 3.5 nm, less than or equal toabout 3.3 nm, or less than or equal to about 3.2 nm. The nickel oxidenanoparticles may have an average particle diameter within the disclosedrange, and uniformity of a film thickness of the first auxiliary layer12 may be increased.

The average particle diameter of the plurality of nickel oxidenanoparticles may be for example greater than or equal to about 1 nm,greater than or equal to about 2 nm, or greater than or equal to about2.5 nm. The nickel oxide nanoparticles may have an average particlediameter within the disclosed ranges, and the first auxiliary layer mayinclude nickel in a sufficient amount to transport holes injected fromthe first electrode.

For example, the average particle diameter of the plurality of nickeloxide nanoparticles may be greater than or equal to about 1 nm and lessthan about 5 nm, greater than or equal to about 1 nm and less than orequal to about 4 nm, greater than or equal to about 1 nm and less thanor equal to about 3.5 nm, greater than or equal to about 1 nm and lessthan or equal to about 3.3 nm, greater than or equal to about 1 nm andless than or equal to about 3.2 nm, greater than or equal to about 2 nmand less than about 5 nm, greater than or equal to about 2 nm and lessthan or equal to about 4 nm, greater than or equal to about 2 nm andless than or equal to about 3.5 nm, greater than or equal to about 2 nmand less than or equal to about 3.3 nm, greater than or equal to about 2nm and less than or equal to about 3.2 nm, greater than or equal toabout 2.5 nm and less than about 5 nm, greater than or equal to about2.5 nm and less than or equal to about 4 nm, greater than or equal toabout 2.5 nm and less than or equal to about 3.5 nm, greater than orequal to about 2.5 nm and less than or equal to about 3.3 nm, or greaterthan or equal to about 2.5 nm and less than or equal to about 3.2 nm.

For example, sizes of a plurality of nickel oxide nanoparticles may bedistributed relatively evenly. For example, about 90% or greater of thetotal number of the nickel oxide nanoparticles included in the firstauxiliary layer 12 may fall within about ±30% range, about ±28% range,about ±26% range, about ±25% range, about ±24% range, about ±23% range,or about ±22% range of the average particle diameter of the nickel oxidenanoparticles. Accordingly, the thickness of the first auxiliary layer12 may be uniform.

For example, a standard deviation of a particle diameter of a pluralityof nickel oxide nanoparticles may be less than or equal to about 2 nm,less than or equal to about 1.7 nm, less than or equal to about 1.4 nm,less than or equal to about 1.2 nm, less than or equal to about 1 nm,less than or equal to about 0.8 nm, or less than or equal to about 0.5nm. The nickel oxide nanoparticles may be nanoparticles consisting ofnickel oxide or including nickel oxide as a main component.

For example, the nickel oxide nanoparticles may be made of nickel oxide,such as for example NiO.

For example, the nickel oxide nanoparticles may include nickel oxide asa main component, and may further include a dopant other than nickel.The dopant may be a metal dopant or a semi-metal dopant and may be forexample a metal dopant. The metal dopant may include for example copper,aluminum, molybdenum, vanadium, iron, lithium, manganese silver, cobalt,zirconium, chromium, zinc, or a combination thereof, but is not limitedthereto.

The dopant may finely deform a crystal structure of nickel oxide, suchthat the crystallinity and a HOMO energy level, LUMO energy level, or acombination thereof of nickel oxide can effectively be controlled.Accordingly, the first auxiliary layer 12 may be adjusted to havedesired electrical characteristics between the first electrode 11 andthe quantum dot layer 14. Accordingly, the performance and stability ofthe light emitting device may be increased.

For example, the metal dopant may be included in an amount of less thanabout 50 wt %, less than or equal to about 40 wt %, less than or equalto about 30 wt %, less than or equal to about 20 wt %, less than orequal to about 15 wt %, less than or equal to about 10 wt %, for exampleabout 0.1 wt % to about 50 wt %, about 0.1 wt % to about 40 wt %, about0.1 wt % to about 30 wt %, about 0.1 wt % to about 20 wt %, about 0.1 wt% to about 15 wt %, or about 0.1 wt % to about 10 wt %, based on a totalweight of the nickel oxide nanoparticles.

The nickel oxide nanoparticles may include the organic ligand that isbound or attached to a surface thereof. The organic ligand may be boundor attached to a surface of nickel oxide nanoparticles to decrease orprevent agglomeration of the nickel oxide nanoparticles in a solvent ordispersive medium, enabling the formation of first auxiliary layer 12through a solution process.

The organic ligand may be derived from a compound with a functionalgroup that may be attached or bound to a surface of the nickel oxide.For example, the organic ligand may be derived from a compound having asubstituted or unsubstituted amine group, a substituted or unsubstitutedcarboxyl group, or a combination thereof, for example a compound havinga aliphatic or aromatic hydrocarbon having a substituted orunsubstituted amine group, an aliphatic or aromatic hydrocarbon having asubstituted or unsubstituted carboxyl group, or a combination thereof.

For example, the aliphatic or aromatic hydrocarbon having a substitutedor unsubstituted amine group and the aliphatic or aromatic hydrocarbonhaving the substituted or unsubstituted carboxyl group may be analiphatic or aromatic hydrocarbon having a relatively low carbon number,for example an aliphatic or aromatic hydrocarbon having a carbon numberof 10 or less, 9 or less, or 8 or less. For example, the organic ligandmay be derived from a substituted or unsubstituted C1 to C10 alkylaminecompound, a substituted or unsubstituted C2 to C10 carboxylic acidcompound, or a combination thereof.

As such, by including the organic ligand, dispersion of the nickel oxidenanoparticles may be improved due to the organic ligand in the coatingprocess and also by including the organic ligand derived from thecompound having the relatively low carbon number, the content of anorganic material remaining in the first auxiliary layer 12 may bereduced, and deterioration of electrical characteristics caused by theorganic ligand may be reduced or prevented.

For example, the substituted or unsubstituted C1 to C10 alkylaminecompound may be, for example, a substituted or unsubstituted C3 to C8alkylamine compound, a substituted or unsubstituted C5 to C8 alkylaminecompound, or a substituted or unsubstituted C6 to C8 alkylaminecompound. For example, the substituted or unsubstituted C2 to C10carboxylic acid compound may be for example, a substituted orunsubstituted C3 to C8 carboxylic acid compound, a substituted orunsubstituted C5 to C8 carboxylic acid compound, or a substituted orunsubstituted C6 to C8 carboxylic acid compound.

For example, the substituted or unsubstituted C1 to C10 alkylaminecompound may be a substituted or unsubstituted pentylamine, asubstituted or unsubstituted hexylamine, a substituted or unsubstitutedheptylamine, a substituted or unsubstituted octylamine, a substituted orunsubstituted nonylamine, or a combination thereof.

For example, the substituted or unsubstituted C2 to C10 carboxylic acidcompound may be a substituted or unsubstituted pentanoic acid, asubstituted or unsubstituted hexanoic acid, a substituted orunsubstituted heptanoic acid, a substituted or unsubstituted octanoicacid, a substituted or unsubstituted nonanoic acid, or a combinationthereof.

For example, the organic ligand may be derived from a substituted orunsubstituted octylamine, a substituted or unsubstituted octanoic acid,or a combination thereof. For example, in the first auxiliary layer 12,an amount of an organic ligand derived from a substituted orunsubstituted octyl amine may be greater than an amount of an organicligand derived from a substituted or unsubstituted octanoic acid.

The first auxiliary layer 12 may include a portion or all of theaforementioned organic ligands. The organic ligand may be attached orbound to the surface of the nickel oxide nanoparticles in the firstauxiliary layer 12, or may be separated from the nickel oxidenanoparticles. For example, the organic ligand may exist between theadjacent nickel oxide nanoparticles.

For example, the organic ligand may be, for example, in an amount ofless than or equal to about 30 volume %, less than or equal to about 25volume %, or less than or equal to about 20 volume %, for example, about1 volume % to about 30 volume %, about 1 volume % to about 25 volume %,about 1 volume % to about 20 volume %, about 5 volume % to about 30volume %, about 5 volume % to about 25 volume %, or about 5 volume % toabout 20 volume %, based on a total volume the first auxiliary layer 12.

For example, the organic ligand may be in an amount of less than orequal to about 30 wt %, for example, less than or equal to about 25 wt%, or less than or equal to about 20 wt %, for example, about 1 wt % toabout 30 wt %, about 1 wt % to about 25 wt %, about 1 wt % to about 20wt %, about 5 wt % to about 30 wt %, about 5 wt % to about 25 wt %, orabout 5 wt % to about 20 wt %, based on a total weight of the firstauxiliary layer 12.

The first auxiliary layer 12 may include the organic ligand within thedisclosed range, the first auxiliary layer 12 may have sufficientinsulating characteristics to decrease or prevent opposite charges fromflowing over from the quantum dot layer 14, and current leakage of thelight emitting device including the first auxiliary layer 12 may bereduced.

For example, the first auxiliary layer 12 may have a thickness, forexample, greater than or equal to about 1 nm, greater than or equal toabout 3 nm, or greater than or equal to about 5 nm, for example, lessthan or equal to about 50 nm, less than or equal to about 40 nm, lessthan or equal to about 30 nm, less than or equal to about 25 nm, or lessthan or equal to about 20 nm, for example, about 1 nm to about 50 nm, orabout 5 nm to about 20 nm. Accordingly, the first auxiliary layer 12 mayeasily transport holes injected from the first electrode 11. If thethickness of the first auxiliary layer 12 is greater than the disclosedrange, it may be difficult for the first auxiliary layer 12 to transportthe holes injected from the first electrode 11 efficiently. In addition,when the thickness of the first auxiliary layer 12 is less than thedisclosed range, it may be difficult for the first auxiliary layer 12 tohave a uniform thickness, and the light emitting device including thefirst auxiliary layer 12 having a thickness less than the disclosedrange may cause a short circuit.

The second auxiliary layer 13 may be disposed between the firstauxiliary layer 12 and the quantum dot layer 14, and may be one layer ortwo or more layers. The second auxiliary layer 13 may be omitted. Thesecond auxiliary layer 13 may include a hole auxiliary layer forexample, for example, a hole transport layer, an electron blockinglayer, or a combination thereof. For example, the second auxiliary layer13 disposed between the first auxiliary layer 12 and the quantum dotlayer 14 may decrease or prevent exciton quenching from occurring at theinterface of first auxiliary layer 12 and quantum dot layer 14, andefficiency deterioration of light emitting devices may be prevented.

The second auxiliary layer 13 may be different from the first auxiliarylayer 12. For example, the first auxiliary layer 12 may have a HOMOenergy level of about 5.0 eV to about 6.0 eV, within the disclosedrange, for example about 5.0 eV to about 5.5 eV. For example, the secondauxiliary layer 13 may have a HOMO energy level of about 5.2 eV to about7.0 eV, within the disclosed range, for example about 5.3 eV to about6.8 eV, about 5.3 eV to about 6.5 eV, about 5.3 eV to about 6.3 eV, orabout 5.3 eV to about 6.1 eV. When the energy levels of the firstauxiliary layer 12 and the second auxiliary layer 13 are as describedherein, holes may be transported to the quantum dot layer 14 moreefficiently, and efficiency of the light emitting device may be furtherimproved.

For example, the second auxiliary layer 13 may include an organicmaterial, an inorganic material, an organic/inorganic material, or acombination thereof, for examplepoly(9,9-dioctyl-fluorene-co-N-(4-butylphenyl)-diphenylamine (TFB),polyarylamine, poly(N-vinylcarbazole, polyaniline, polypyrrole,N,N,N′,N′-tetrakis(4-methoxyphenyl)-benzidine (TPD),(4-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl (α-NPD), m-MTDATA(4,4′,4″-tris[phenyl(m-tolyl)amino]triphenylamine),4,4′,4″-tris(N-carbazolyl)-triphenylamine (TCTA),1-bis[(di-4-tolylamino)phenylcyclohexane (TAPC), p-type metal oxide(e.g., NiO, WO₃, MoO₃, etc.), a carbon-based material such as grapheneoxide, or a combination thereof, but is not limited thereto.

For example, the second auxiliary layer 13 may include an organicmaterial, for example,poly(9,9-dioctyl-fluorene-co-N-(4-butylphenyl)-diphenylamine (TFB), butis not limited thereto.

For example, the second auxiliary layer 13 may have a thickness, forexample, greater than or equal to about 1 nm, greater than or equal toabout 3 nm, or greater than or equal to about 5 nm, for example, lessthan or equal to about 50 nm, less than or equal to about 40 nm, lessthan or equal to about 30 nm, less than or equal to about 25 nm, or lessthan or equal to about 20 nm, for example, about 1 nm to about 50 nm, orabout 5 nm to about 20 nm. Accordingly, the second auxiliary layer 13may easily transfer holes injected or transported from the firstauxiliary layer 12. If the thickness of the second auxiliary layer 13 isgreater than the disclosed range, it may be difficult for the secondauxiliary layer 13 to transport holes injected from the first auxiliarylayer 12 efficiently. In addition, when the thickness of the secondauxiliary layer 13 is less than the disclosed range, it may be difficultfor the second auxiliary layer 13 to have a uniform thickness, and alight emitting device including the first auxiliary layer 12 having athickness less than the disclosed range may cause a short circuit.

Optionally, an additional layer (not shown) may be further includedbetween the first electrode 11 and the quantum dot layer 14. Forexample, the additional layer may be further included between the firstelectrode 11 and the first auxiliary layer 12, the additional layer maybe further included between the first auxiliary layer 12 and secondauxiliary layer 13, an additional layer may be further included betweenthe second auxiliary layer 13 and the quantum dot layer 14, or acombination thereof.

The third auxiliary layer 15 may be disposed between the quantum dotlayer 14 and the second electrode 16 and may be one layer or two or morelayers. The third auxiliary layer 15 may be omitted. The third auxiliarylayer 15 may include an example, an electron auxiliary layer, forexample, an electron injection layer, an electron transport layer, ahole blocking layer, or a combination thereof.

For example, the third auxiliary layer 15 may have a HOMO energy levelthat is higher or lower than the HOMO energy of the quantum dot layer14. For example, the third auxiliary layer 15 may have a HOMO energylevel of greater than or equal to about 4.5 eV, greater than or equal toabout 5 eV, greater than or equal to about 5.5 eV, greater than or equalto about 6 eV, greater than or equal to about 6.5 eV, greater than orequal to about 6.6 eV, greater than or equal to about 6.7 eV, greaterthan or equal to about 6.8 eV, greater than or equal to about 6.9 eV,greater than or equal to about 7 eV, greater than or equal to about 7.1eV, greater than or equal to about 7.2 eV, greater than or equal toabout 7.3 eV, greater than or equal to about 7.4 eV, greater than orequal to about 7.5 eV, greater than or equal to about 7.6 eV, greaterthan or equal to about 7.7 eV, greater than or equal to about 7.8 eV,greater than or equal to about 7.9 eV, or greater than or equal to about8.0 eV, for example, less than or equal to about 9.5 eV, or less than orequal to about 9.0 eV, or less than or equal to about 8.5 eV.

For example, the third auxiliary layer 15 may have a LUMO energy levelthat is higher than the LUMO energy level of the quantum dot layer 14.For example, the third auxiliary layer 15 may have a LUMO energy levelof greater than or equal to about 2.5 eV, greater than or equal to about3.0 eV, greater than or equal to about 3.5 eV, or greater than or equalto about 4.0 eV, for example less than or equal to about 7.0 eV, lessthan or equal to about 6.5 eV, less than or equal to about 6.0 eV, lessthan or equal to about 5.5 eV, less than or equal to about 5.0 eV, orless than or equal to about 4.5 eV.

The electron transport layer, the electron injection layer, or acombination thereof may include, for example an organic material, aninorganic material, an organic/inorganic material, or a combinationthereof, for example 1,4,5,8-naphthalene-tetracarboxylic dianhydride(NTCDA), bathocuproine (BCP), tris[3-(3-pyridyl)-mesityl]borane(3TPYMB), LiF, Alq₃, Gaq₃, Inq₃, Znq₂, Zn(BTZ)₂, BeBq₂, ET204(8-(4-(4,6-di(naphthalen-2-yl)-1,3,5-triazin-2-yl)phenyl)quinolone),8-hydroxyquinolinato lithium (Liq), an n-type metal oxide (e.g., ZnO,HfO₂, etc.), or a combination thereof, but is not limited thereto.

The hole blocking layer may include, for example an organic material, aninorganic material, an organic/inorganic material, or a combinationthereof, for example 1,4,5,8-naphthalene-tetracarboxylic dianhydride(NTCDA), bathocuproine (BCP), tris[3-(3-pyridyl)-mesityl]borane(3TPYMB), LiF, Alq₃, Gaq₃, Inq₃, Znq₂, Zn(BTZ)₂, BeBq₂, or a combinationthereof, but is not limited thereto.

For example, the third auxiliary layer 15 may include an electrontransport layer and may increase transport of electrons from the secondelectrode 16 to the quantum dot layer 14.

For example, the third auxiliary layer 15 may include an n-type metaloxide, for example, an n-type metal oxide nanoparticle.

For example, the third auxiliary layer 15 may include a zinc oxidenanoparticle. The zinc oxide may be an oxide including zinc as a maincomponent and optionally, doped with another metal or semi-metal and maybe, for example, represented by Zn_(1-x)M_(x)O (wherein M is Mg, Ca, Zr,W, Li, Ti, or a combination thereof, and 0≤x<0.5).

For example, M may be Mg, Co, Ni, or a combination thereof, and x may bein a range of about 0.01≤x≤0.4, about 0.02≤x≤0.4, about 0.03≤x≤0.3, orabout 0.05≤x≤0.3.

For example, the zinc oxide nanoparticle may have an average particlediameter, for example, greater than or equal to about 1 nm, greater thanor equal to about 1.5 nm, greater than or equal to about 2 nm, greaterthan or equal to about 2.5 nm, or greater than or equal to about 3 nm,for example, less than or equal to about 10 nm, less than or equal toabout 9 nm, less than or equal to about 8 nm, less than or equal toabout 7 nm, less than or equal to about 6 nm, or less than or equal toabout 5 nm.

For example, the zinc oxide nanoparticles may be ZnO nanoparticles,Zn_(1-x)Mg_(x)O nanoparticles, or a combination thereof. The zinc oxidenanoparticles may not be in the form of rods or nanowires.

For example, a thickness of the third auxiliary layer 15 (e.g., each ofelectron injection layer, electron transport layer, or hole blockinglayer) may be, for example greater than or equal to about 5 nm, greaterthan or equal to about 6 nm, greater than or equal to about 7 nm,greater than or equal to about 8 nm, greater than or equal to about 9nm, greater than or equal to about 10 nm, greater than or equal to about11 nm, greater than or equal to about 12 nm, greater than or equal toabout 13 nm, greater than or equal to about 14 nm, greater than or equalto about 15 nm, greater than or equal to about 16 nm, greater than orequal to about 17 nm, greater than or equal to about 18 nm, greater thanor equal to about 19 nm, or greater than or equal to about 20 nm, andfor example less than or equal to about 120 nm, less than or equal toabout 110 nm, less than or equal to about 100 nm, less than or equal toabout 90 nm, less than or equal to about 80 nm, less than or equal toabout 70 nm, less than or equal to about 60 nm, less than or equal toabout 50 nm, less than or equal to about 40 nm, less than or equal toabout 30 nm, or less than or equal to about 25 nm, but is not limitedthereto.

Optionally, an additional layer (not shown) may be further includedbetween the second electrode 16 and the quantum dot layer 14. Forexample, an additional layer may be further included between the secondelectrode 16 and the third auxiliary layer 15, or an additional layermay be further included between the third auxiliary layer 15 and thequantum dot layer 14.

An embodiment provides a method of manufacturing the aforementionedlight emitting device.

The method of manufacturing the aforementioned light emitting device 10includes forming first electrode 11 on a substrate (not shown), formingfirst auxiliary layer 12 on the first electrode 11, forming a secondauxiliary layer 13 on the first auxiliary layer 12, forming a quantumdot layer 14 on the second auxiliary layer 13, forming a third auxiliarylayer 15 on the quantum dot layer 14, and forming a second electrode 16on the third auxiliary layer 15. In this case, the forming of the secondauxiliary layer 13 and the forming of the third auxiliary layer 15 maybe omitted.

The first auxiliary layer 12, second auxiliary layer 13, quantum dotlayer 14 and third auxiliary layer 15 may be formed by a solutionprocess, respectively, for example a spin coating, a slit coating, aninkjet printing, a nozzle printing, a spraying, a doctor blade coating,or a combination thereof, but is not limited thereto.

The forming of the first auxiliary layer 12 may be performed by asolution process, and may be performed by an example a spin coating, aspray coating, a slit coating, a dip coating, an inkjet printing, anozzle printing, a doctor blade coating, or a combination thereof, butis not limited thereto.

For example, the forming of the auxiliary layer 12 may include obtainingthe nickel oxide nanoparticles and organic ligand from a precursormixture including a nickel oxide precursor and an organic ligandprecursor, and obtaining a composition for a first auxiliary layerincluding the nickel oxide nanoparticles and organic ligand, and coatingthe composition for the first auxiliary layer.

The nickel oxide precursor may include nickel (II) acetylacetonate andin an embodiment may not include nickel (II) acetate, nickel nitrate, ora combination thereof.

For example, the organic ligand precursor may be a substituted orunsubstituted C1 to C10 alkylamine compound, a substituted orunsubstituted C2 to C10 carboxylic acid compound, or a combinationthereof. Specifically, the substituted or unsubstituted C1 to C10alkylamine compound, and the substituted or unsubstituted C2 to C10carboxylic acid compound are the same as described herein.

For example, the organic ligand precursor may be a substituted orunsubstituted octylamine, a substituted or unsubstituted octanoic acid,or a combination thereof.

Optionally, the precursor mixture may further include a dopantprecursor. The dopant precursor may include a metal of copper, aluminum,molybdenum, vanadium, iron, lithium, manganese silver, cobalt,zirconium, chromium, zinc, or a combination thereof and may include, forexample, an acetylacetonate including the metal.

Optionally, the precursor mixture may further include a reactioncatalyst.

In an embodiment, the precursor mixture may not include a separatedispersing agent to disperse the nickel oxide nanoparticles. Forexample, in an embodiment, the precursor mixture may not include aninorganic dispersing agent and an organic dispersing agent such as ametal salt in order to disperse metal nanoparticles. Accordingly, in anembodiment, the first auxiliary layer 12 prepared from the precursormixture may not include a dispersing agent, and deterioration of drivingcharacteristics caused by a dispersing agent of the light emittingdevice including the first auxiliary layer 12 may be decreased orprevented.

The dopant precursor in the precursor mixture may be present in anamount of about 1 mole percent (mol %) to about 20 mol %, for example,about 3 mol % to about 20 mol %, based on the total number of moles ofthe nickel oxide precursor and dopant precursor. When the precursormixture includes the dopant precursor within the disclosed range, thefirst auxiliary layer 12 may be controlled to have sufficient electricalcharacteristics between the first electrode 11 and the quantum dot layer14. If the precursor mixture includes the dopant precursor in an amountgreater than the disclosed range, injection of holes moving from thefirst electrode 11 to the quantum dot layer 14, migrationcharacteristics of holes moving from the first electrode 11 to thequantum dot layer 14, or a combination thereof may decrease.

Herein, the number of moles of the substituted or unsubstituted C1 toC10 alkylamine compound of the organic ligand precursor may be higherthan that of substituted or unsubstituted C2 to C10 carboxylic acidcompound.

For example, the obtaining of the nickel oxide nanoparticles and organicligand may include, for example, heat-treating the precursor mixture ata temperature of less than or equal to about 150° C., less than or equalto about 140° C., less than or equal to about 130° C., less than orequal to about 125° C., or less than or equal to about 120° C. and mayinclude for example heat-treating the same at a temperature of greaterthan or equal to about 50° C., greater than or equal to about 60° C.,greater than or equal to about 70° C. greater than or equal to about 75°C., or greater than or equal to about 80° C. For example, the obtainingof the nickel oxide nanoparticles and organic ligand may includeheat-treating the same at a temperature of about 50° C. to about 150°C., or about 80° C. to about 120° C.

For example, in an embodiment, the obtaining of the nickel oxidenanoparticles may not include a sol-gel process, which may include ahigh temperature process, and nickel oxide nanoparticles having asmaller average particle diameter and a more uniform distribution of aparticle diameter at a relatively low temperature may be obtained.

For example, the nickel oxide nanoparticles and the organic ligandobtained from the precursor mixture including the nickel oxide precursorand organic ligand precursor may be bound, attached, or a combinationthereof to each other. For example, the organic ligand may be bound,attached, or a combination thereof to the surface of the nickel oxidenanoparticles. Accordingly, the composition for the first auxiliarylayer in which nickel oxide nanoparticles are not agglomerated may beformed even without a dispersing agent.

The composition for the first auxiliary layer may include a solvent, andthe solvent, which should be capable of dispersing the organic ligandand nickel oxide nanoparticles, organic ligand, or a combinationthereof, is not limited.

For example, when the organic ligand is derived from an unsubstituted C1to C10 alkylamine compound or an unsubstituted C1 to C10 carboxylic acidcompound, the solvent included in the composition for forming the firstauxiliary layer may be an organic solvent. Herein, the organic solventmay include C5 to C16 alkane, for example, C6 to C10 alkane or C6 to C8alkanes. By including the alkane in the carbon number range, the nickeloxide nanoparticles in the composition for the first auxiliary layer maybe dispersed without agglomeration, and the amount of the organic ligandin the first auxiliary layer 12 may be controlled even by heat treatmentat a relatively low temperature.

For example, the organic solvent included in the composition for formingthe first auxiliary layer may be a substituted or unsubstituted hexane,a substituted or unsubstituted heptane, a substituted or unsubstitutedoctane, or a substituted or unsubstituted nonane, but is not limitedthereto.

When the organic ligand is derived from a C1 to C10 alkylamine compoundfurther including a hydrophilic substituent other than an amino group oran unsubstituted C1 to C10 carboxylic acid compound further including ahydrophilic substituent other than a carboxyl group, a solvent includedin the composition for forming the first auxiliary layer may be ahydrophilic solvent. Herein, the hydrophilic solvent may include forexample an alcohol solvent, for example methanol, ethanol, isopropanol,butanol, or a combination thereof.

For example, the coating the composition for the first auxiliary layermay include a spin coating, a spray coating, a slit coating, a dipcoating, an inkjet printing, a nozzle printing, a doctor blade coating,or a combination thereof of the composition for the first auxiliarylayer.

For example, the coating of the composition for the first auxiliarylayer may include heat-treating at a temperature of less than or equalto about 500° C. less than or equal to about 450° C., less than or equalto about 400° C., less than or equal to about 350° C., less than orequal to about 320° C., less than or equal to about 300° C., less thanor equal to about 270° C., less than or equal to about 250° C., lessthan or equal to about 230° C., less than or equal to about 220° C.,less than or equal to about 210° C., or less than or equal to about 200°C.

According to an embodiment, a display device including theaforementioned light emitting device may be provided, and the lightemitting device may be applied to not only a display device but alsovarious electronic devices such as lighting devices, and the like.

Hereinafter, the embodiments are illustrated in more detail withreference to examples. However, these examples are exemplary, and thepresent scope is not limited thereto.

EXAMPLES Synthesis Example: Synthesis of Quantum Dot (1) Synthesis ofInP Core

0.2 millimoles (mmol) of Indium acetate, 0.6 mmol of palmitic acid, and10 milliliters (mL) of 1-octadecene are put in a reactor and then,heated at 120° C. under vacuum. After 1 hour, an atmosphere in thereactor is converted into nitrogen. The reactor is heated at 280° C., amixed solution of 0.1 mmol of tris(trimethylsilyl)phosphine (TMS3P) and0.5 mL of trioctylphosphine is rapidly injected thereinto and then,reacted for 20 minutes. The reaction solution is rapidly cooled down toroom temperature, acetone is added thereto and centrifuged, and then,precipitates obtained therefrom are dispersed in toluene to obtain InPtoluene dispersion.

(2) Synthesis of InP Core/ZnS Shell Quantum Dot

0.3 mmoL (0.056 grams (g)) of zinc acetate, 0.6 mmol (0.189 g) of oleicacid, and 10 mL of trioctylamine are put in a reaction flask and then,vacuum-treated at 120° C. for 10 minutes. The reaction flask isinternally substituted with N₂ and then, heated up to 220° C.Subsequently, the InP toluene dispersion (OD: 0.15) according toSynthesis Example and 0.6 mmol of S/TOP are put in the reaction flaskand then, heated up to 280° C. and reacted for 30 minutes. When areaction is complete, the reaction solution is rapidly cooled down toroom temperature, an excessive amount of ethanol is added thereto andthen, centrifuged to remove an extra organic material present in thequantum dot reactant. After the centrifugation, a supernatant isdiscarded, the precipitates are dissolved again in hexane, and anexcessive amount of ethanol is added thereto and then, centrifugedagain. The centrifuged precipitates are dried and dispersed again inoctane to obtain InP/ZnS core shell quantum dot dispersion.

Preparation of Composition for First Auxiliary Layer (1) Preparation ofComposition 1 for First Auxiliary Layer

Nickel acetylacetonate (C₁₀H₁₄NiO₄, 1 mmol), octylamine (C₈H₁₉N, 15 mL),and octanoic acid (C₈H₁₆O₂, 1 mmol) are put in a reactor, vigorouslystirred at 110° C. for 30 minutes, and then, cooled down to 90° C.Subsequently, a borane-triethyl complex ((C₂H₅)₃NBH₃, 2.4 mmol) is addedthereto and then, reacted at 90° C. for 1 hour and cooled down to roomtemperature. 30 mL of ethanol is added thereto and then, centrifuged at5,000 to 7,000 rpm to obtain NiO nanoparticles as precipitates. Theobtained NiO nanoparticles are washed with ethanol and acetone and then,dispersed at a level of 0.5 to 50 milligrams per milliliter (mg/mL) inoctane to prepare nickel oxide nanoparticle dispersion.

(2) Preparation of Composition 2 for First Auxiliary Layer

Nickel acetylacetonate (C₁₀H₁₄NiO₄, 0.9 mmol), copper (II)acetylacetonate (C₁₀H₁₄CuO₄, 0.1 mmol), octylamine (C₈H₁₉N, 5 mL), andoctanoic acid (C8H16O2, 1 mmol) are put in a reactor and then,vigorously stirred at 110° C. for 30 minutes and cooled down to 90° C.Subsequently, a borane-triethyl complex ((C₂H₅)₃NBH₃, 2.4 mmol) is addedthereto and then, reacted at 90° C. for 1 hour and cooled down to roomtemperature. 30 mL of ethanol is added thereto and then, centrifuged at5,000 to 7,000 rpm to obtain NiO nanoparticles as precipitates. Theobtained NiO nanoparticles are washed with ethanol and acetone and then,dispersed in octane at a level of 0.5 to 50 mg/mL to prepare Cu-dopednickel oxide nanoparticle dispersion.

(3) Preparation of Reference Composition for First Auxiliary Layer

Nickel acetylacetonate (C₁₀H₁₄NiO₄, 1 mmol), oleylamine (C₁₈H₃₇N, 15mL), and oleic acid (C₁₈H₃₄O₂, 1 mmol) are put in a reactor and then,fervently stirred at 110° C. for 30 minutes and cooled down to 90° C.Subsequently, a borane-triethyl complex ((C₂H₅)₃NBH₃, 2.4 mmol) is addedthereto and then, reacted at 90° C. for 1 hour and cooled down to roomtemperature. 30 mL of ethanol is added thereto and then, centrifuged at5,000 to 7,000 rpm to obtain NiO nanoparticles as precipitates. Theobtained NiO nanoparticles are washed with ethanol and acetone and then,dispersed in octane at a level of 0.5 to 50 mg/mL to prepare nickeloxide nanoparticle dispersion.

(4) Preparation of Comparative Composition for First Auxiliary Layer

Nickel oxide (NiO) nanoparticles are synthesized in a spray flamemethod. To prepare a precursor, 2-ethylhexanoic acid (1080 g,Sigma-Aldrich Co., Ltd.) and Ni-acetate 4-hydrate (269.2 g,Sigma-Aldrich Co., Ltd.) are heated and dissolved at 150° C. for 1 hour.Subsequently, tetrahydrofuran (540 g, Sigma-Aldrich Co., Ltd.) is addedthereto to prepare a precursor mixture. Then, the precursor mixture issupplied in a spray nozzle (7 milliliters per minute (ml/min), a microcyclic gear pump mzr-2900 manufactured by HNP microsystem GmbH) anddispersed by oxygen (15 liters per minute (L/min), PanGas Tech) andignited with premixed methane-oxygen flame (CH₄: 1.2 L/min, O₂: 2.2L/min). Subsequently, the discharged gas is filtered with a glass fiberfilter (Schleicher & Schuell) by a vacuum pump (Seco SV1040CV, Busch) atabout 20 cubic meters per hour (m³/h) to obtain nickel oxidenanoparticle powders. The obtained nickel oxide nanoparticle powders arecollected from the glass fiber filter.

5 weight percent (wt %) of the obtained nickel oxide nanoparticlepowders, 0.1 wt % of yttrium (Ill) nitrate 6-hydrate (Sigma Aldrich Co.,Ltd.), and 94.9 wt % of methanol (Merck Co., Inc.) are mixed to preparea solution, and then, the solution is dispersed through ball-milling for1 hour to prepare a comparative composition for a first auxiliary layer.

Manufacture of Thin Film Preparation Example 1

100 microliters (μL) to 200 μL of the composition 1 for the firstauxiliary layer is spin-coated on a glass plate and dried to obtain a 10nanometers (nm) to 15 nm-thick thin film.

Preparation Example 2

The thin film of Preparation Example 1 is additionally heat-treated at200° C. for 20 minutes to form a 10 nm to 15 nm-thick thin film.

Preparation Example 3

The thin film of Preparation Example 1 is additionally heat-treated at500° C. for 60 minutes to form a 15 nm-thick thin film.

Preparation Example 4

100 μL to 200 μL of the composition 2 for a first auxiliary layer isspin-coated on a glass plate and dried to obtain a 10 nm to 15 nm-thickthin film.

Preparation Example 5

The thin film of Preparation Example 4 is additionally heat-treated at200° C. for 20 minutes to form a 10 nm to 15 nm-thick thin film.

Preparation Example 6

The thin film of Preparation Example 4 is additionally heat-treated at500° C. for 60 minutes to form a 10 nm to 15 nm-thick thin film.

Reference Preparation Example 1

100 μL to 200 μL of the reference composition for a first auxiliarylayer is spin-coated on a glass plate and dried to obtain a 10 nm to 15nm-thick thin film.

Reference Preparation Example 2

The thin film of Reference Preparation Example 1 is additionallyheat-treated at 200° C. for 20 minutes to form a 10 nm to 15 nm-thickthin film.

Reference Preparation Example 3

The thin film of Reference Preparation Example 1 is additionallyheat-treated at 500° C. for 60 minutes to form a 10 nm to 15 nm-thickthin film.

Comparative Preparation Example 1

100 μL to 200 μL of the composition 2 for a first auxiliary layer isspin-coated on a glass plate and dried to obtain a 10 nm to 15 nm-thickthin film.

Comparative Preparation Example 2

The thin film of Comparative Preparation Example 1 is additionallyheat-treated at 200° C. for 20 minutes to form a 10 nm to 15 nm-thickthin film.

Comparative Preparation Example 3

The thin film of Comparative Preparation Example 1 is additionallyheat-treated at 500° C. for 60 minutes to form a 10 nm to 15 nm-thickthin film.

Thin Film Evaluation I

Crystalline and morphology of the thin films of Preparation Examples andReference Preparation Examples are evaluated.

The crystalline and morphology of the thin films are evaluated by usinga transmission electron microscope (TEM, JEM-2100 Electron Microscopemanufactured by JEOL Inc.) and a scanning electron microscope (SEM,JSM-7900F manufactured by JEOL Inc.).

FIG. 2 is a transmission electron microscopic (TEM) image showing themorphology of the thin film of Preparation Example 1,

FIG. 3 is a transmission electron microscopic (TEM) image showing themorphology of the thin film of Preparation Example 2,

FIG. 4 is a scanning electron microscopic (SEM) image showing themorphology of the thin film of Reference Preparation Example 1, and

FIG. 5 is a scanning electron microscopic (SEM) image showing themorphology of the thin film of Reference Preparation Example 2.

In FIGS. 2 to 5, a relatively bright region indicates nickel oxidenanoparticles, but a relatively dark region indicates an organic ligand.

A plurality of nickel oxide nanoparticles included in the thin film hasan average particle diameter obtained by randomly selecting a 100 nm×100nm-sized square range in the TEM or SEM image of the thin films,measuring particle diameters of all the nickel oxide nanoparticleswithin the square range, and dividing a sum of the a particle diametersof the nickel oxide nanoparticles by the number of the nickel oxideparticles.

Referring to FIGS. 2 to 5, the thin films of Preparation Examples 1 and2 and Reference Preparation Examples 1 and 2 include a plurality ofnickel oxide nanoparticles of less than or equal to about 10 nm, and theplurality of nickel oxide nanoparticles included in the thin film has acubic crystal structure. Referring to FIG. 3, the thin film ofPreparation Example 2 has a particle diameter within a narrow range ofabout 2 nm to 4 nm, and specifically, the nickel oxide nanoparticlesturn out to have an average particle diameter of about 3.2 nm. Inaddition, greater than or equal to 90% of all the nickel oxidenanoparticles have an average particle diameter within a range of ±30%and a standard deviation of about 0.8 nm.

Accordingly, the thin films of Preparation Examples 1 and 2 andReference Preparation Examples 1 and 2 include a plurality of nanoparticles having a relatively uniform particle size of less than about 5nm.

In addition, the thin film of Preparation Example 2 includes lessorganic ligands and more uniformly distributed nickel oxidenanoparticles than the thin film of Reference Preparation Example 2.

Thin Film Evaluation II

Organic ligand amounts of the thin films of Preparation Examples andReference Preparation Examples are evaluated.

The organic ligand amounts are evaluated through a thermogravimetric(TGA) analysis.

First, the organic ligand amounts of the thin films of PreparationExamples 1 and 4 and Reference Preparation Example 1 are evaluated. Theorganic ligand amounts are evaluated by respectively measuring weights(initial weights before a heat treatment) of the thin films ofPreparation Examples 1 and 4 and Reference Preparation Example 1 andweights (weights after the heat treatment at 500° C.) of the thin filmsof Preparation Examples 3 and 6 and Reference Preparation Example 3 andthen, calculating weight differences between them.

Organic ligand amount (%)={(Initial weight−Weight after heat treatmentat 500° C.)/Initial weight}×100%  Calculation Equation 1

TABLE 1 Organic ligand amount (wt %) Preparation 25.9 Example 1Preparation 26.6 Example 4 Reference 38 Preparation Example 1

Referring to Table 1, the thin films of Preparation Examples 1 and 4include a lesser amount of organic ligand than that of the thin film ofReference Preparation Example 1.

Subsequently, weight changes depending on a temperature of the films ofPreparation Examples 1 and 4 and Reference Preparation Example 1 areevaluated. Specifically, the weights (initial weights) of the thin filmsof Preparation Examples 1 and 4 and Reference Preparation Example 1 arerespectively measured, and the weight changes of the films are measuredwhile respectively heated up to 600° C.

FIG. 6 is a temperature-weight variation ratio graph showing weightvariation ratios depending on a temperature of the thin films ofPreparation Examples 1 and 4 and Reference Preparation Example 1.

The weight variation ratios are calculated according to CalculationEquation 2.

Weight variation (%)=(weight after heat treatment/initialweight)×100%  Calculation Equation 2

Referring to FIG. 8, the thin films of Preparation Examples 1 and 4exhibit a great weight decrease at less than or equal to 200° C., butthe thin film of Reference Preparation Example 1 exhibits no greatweight change at a less than or equal to 200° C. Accordingly, since theorganic ligand amount of the thin films of Preparation Examples 1 and 4is sufficiently decreased at a low temperature compared with the thinfilm of Reference Preparation Example 1 to obtain a light emittingdevice easily-applicable at a lower temperature.

Device Example I: Manufacture of Light Emitting Device 1 Example 1

An indium-tin oxide (ITO) layer is deposited on a glass substrate, andthe composition 1 for a first auxiliary layer is spin-coated andheat-treated at 200° C. for 20 minutes to form a 13 nm-thick firstauxiliary layer. On the first auxiliary layer,poly[(9,9-dioctylfluorenyl-2,7-diyl-co(4,4′-(N-4-butylphenyl)diphenylamine] (TFB, Sumitomo Chemical Co., Ltd.)is dissolved to be 0.1 to 1 wt % in ortho-xylene (o-xylene), and thesolution is spin-coated and then, heat-treated at 150° C. for 30 minutesto form a 10 nm-thick second auxiliary layer. On the second auxiliarylayer, the InP/ZnS core shell quantum dot according to Synthesis Exampleis spin-coated and then, heat-treated at 90° C. to 120° C. for 30minutes to form a 20 nm-thick quantum dot layer. Thereon, Zn₈₅Mg₁₅Onanoparticles (an average particle diameter: 3 to 7 nm) are dissolved inethanol, and Zn₈₅Mg₁₅O dispersion (10 to 100 mg/mL) obtained therefromis spin-coated and then, heat-treated at 120° C. for 30 minutes to forma third auxiliary layer. Subsequently, a 100 nm-thick aluminum thin filmis deposited through sputtering to manufacture a light emitting device.

Reference Example 1

A light emitting device is manufactured according to the same method asExample 1 except that the reference composition for a first auxiliarylayer is used instead of the composition 1 for a first auxiliary layer.

Comparative Example 1

A light emitting device is manufactured according to the same method asExample 1 except that the first auxiliary layer is not formed.

Comparative Example 2

A light emitting device is manufactured according to the same method asExample 1 except that comparative composition for a first auxiliarylayer is spin-coated and heat-treated at 400° C. for 20 minutes insteadof spin-coating and then, heat-treating the composition 1 for a firstauxiliary layer at 200° C. for 20 minutes.

Light Emitting Device Evaluation I

Luminance characteristics and electrical characteristics of the lightemitting devices of Example 1, Reference Example 1, and ComparativeExample 2.

The luminance characteristics and electrical characteristics areevaluated by using a Keithley 220 current source and a Minolta CS200spectroradiometer.

The results are shown in Table 2.

TABLE 2 Maximum Maximum luminance current (candelas per efficiencyV@1000 square meter (candela/ampere nit EQE_(max) (cd/m²)) (cd/A))(volts (V)) Example 1 5.1 47220 4.1 7.4 Reference 1.5 13240 1.3 9.6Example 1 Comparative 1.0 580 — — Example 2 * EQE_(max): maximumexternal quantum efficiency * V@1000 nt: voltage at 1000 nit (cd/m²)

Referring to Table 2, the light emitting device of Example 1 exhibitsexcellent electrical characteristics and luminance characteristics suchas EQE_(max), maximum luminance, maximum current efficiency, V@1000nit,and the like in terms of luminance performance, compared with those ofReference Example 1 and Comparative Example 2.

Light Emitting Device Evaluation II

Life-span characteristics of the light emitting devices of Example 1 andComparative Example 2 are evaluated.

The life-span characteristics are evaluated by driving the lightemitting devices of Example 1 and Comparative Example 2 for 600 hoursand measuring luminance changes thereof. The results are shown in Table3 and FIG. 7.

FIG. 7 is a graph showing life-span characteristics of the lightemitting devices of Example 1 and Comparative Example 1.

TABLE 3 T95 luminance decrease (%) (hours) after 600 hours Example 1 4810 Comparative 5.6 34 Example 1 * T95: time when luminance is reduceddown to 95% of initial luminance

Referring to Table 3 and FIG. 7, the light emitting device of Example 1exhibits improved life-span characteristics compared with the lightemitting device according to Comparative Example 1.

Device Example II: Manufacture of Light Emitting Device 2 Example 2

A light emitting device is manufactured according to the same method asExample 1 except that poly(9-vinylcarbazole) (PVK) instead of thepoly[(9,9-dioctylfluorenyl-2,7-diyl-co(4,4′-(N-4-butylphenyl)diphenylamine] (TFB, Sumitomo Chemical Co., Ltd.)is dissolved to be 0.1 to 1 wt % in o-xylene, and the solution isheat-treated at 150° C. to 200° C. for 30 minutes to form a 10 nm-thicksecond auxiliary layer.

Example 3

A light emitting device is manufactured according to the same method asExample 2 except that the surface of the first auxiliary layer istreated for one minute with a solution prepared by dissolving ZnCl₂ at aconcentration of 50 mg/mL in ethanol before forming the second auxiliarylayer.

Example 4

A light emitting device is manufactured according to the same method asExample 2 except that the surface of the first auxiliary layer istreated for one minute with a solution prepared by dissolvingtetramethylammonium hydroxide (TMAH) at a concentration of 50 mg/mL inethanol before forming the second auxiliary layer.

Comparative Example 3

A light emitting device is manufactured according to the same method asExample 1 except that a 13 nm-thick first auxiliary layer is formed bydissolving poly(3,4-ethylenedioxythiophene) (PEDOT) to be 0.5 wt % ino-xylene and then, spin-coating and heat-treating the solution at 150°C. for 30 minutes instead of spin-coating the composition for the firstauxiliary layer 1 and heat-treating it at 200° C. for 20 minutes toform, and a 10 nm-thick second auxiliary layer is formed by dissolvingpoly(9-vinylcarbazole) (PVK) to 0.5 wt % in o-xylene and spin-coatingthe solution and heat-treating it at 150° C. for 30 minutes instead ofdissolving the poly[(9,9-dioctylfluorenyl-2,7-diyl-co(4,4′-(N-4-butylphenyl)diphenylamine] (TFB, Sumitomo Chemical Co., Ltd.)to be 0.5% in o-xylene and then, spin-coating the solution andheat-treating it at 150° C. to 200° C. for 30 minutes.

Light Emitting Device Evaluation III

Life-span characteristics of the light emitting devices of Examples 2 to4 and Comparative Example 3 are evaluated.

The life-span characteristics are evaluated by driving the lightemitting devices of Examples 2 to 4 and Comparative Example 3 for 400hours and measuring luminance changes thereof. The results are shown inFIGS. 8 and 9.

FIGS. 8 and 9 are graphs showing life-span characteristics of the lightemitting devices of Examples 2 to 4 and Comparative Example 3.

Referring to FIGS. 8 and 9, the light emitting devices of Examples 2 to4 exhibit improved life-span characteristics compared with the lightemitting device according to Comparative Example 3.

Device Example III: Manufacture of HOD (Hole Only Device) Example 5

An indium-tin oxide (ITO) layer is deposited on a glass substrate, andthe composition 1 for a first auxiliary layer is spin coated and heattreated at 200° C. for 20 minutes to form a 13 nm-thick first auxiliarylayer. Thereon, the InP/ZnS core shell quantum dot according toSynthesis Example is spin-coated and then, heat-treated at 80° C. to130° C. for 30 minutes to form a 20 nm-thick quantum dot layer. On thequantum dot layer, GSH0137 (Novaled GmbH) is deposited at 400 to 550° C.to form a 36 nm-thick GSH layer. On the GSH layer, L101 (LG Chem) isdeposited at 400 to 550° C. to form a 10 nm-thick L101 layer.Subsequently, a 100 nm-thick aluminum thin film is sputtered anddeposited to manufacture a light emitting device.

Example 6

On a glass substrate, an indium-tin oxide (ITO) layer is deposited, andthe composition 1 for a first auxiliary layer is spin coated thereon andheat-treated at 200° C. for 20 minutes to form a 13 nm-thick firstauxiliary layer. Then, a 100 nm-thick aluminum thin film is sputteredand deposited to manufacture a sample device.

Example 7

A light emitting device is manufactured according to the same method asExample 6 except that the composition 2 for a first auxiliary layer isused instead of the composition 1 for a first auxiliary layer.

Reference Example 2

A light emitting device is manufactured according to the same method asExample 2 except that the reference composition for a first auxiliarylayer is used instead of the composition 1 for a first auxiliary layer.

Reference Example 3

A light emitting device is manufactured according to the same method asExample 3 except that the reference composition for a first auxiliarylayer is used instead of the composition 1 for a first auxiliary layer.

HOD Device Evaluation I

Electrical characteristics of the HOD devices of Example 5 and ReferenceExample 2 are evaluated.

The electrical characteristics are evaluated by using a Keithley 220current source and a Minolta CS200 spectroradiometer and then, measuringa current (milliamperes (mA)) at a voltage of 8 V.

The results are shown in Table 4.

TABLE 4 Current (mA) Example 5 0.84 Reference 0.09 Example 2

Referring to Table 4, the thin film of Example 5 has excellentelectrical characteristics compared with the thin film of ReferenceExample 2.

HOD Device Evaluation II

Electrical characteristics of the thin films of Examples 6 and 7 andReference Example 3 are evaluated.

The electrical characteristics are evaluated by using a Keithley 220current source and a Minolta CS200 spectroradiometer and then, measuringa current (mA) at a voltage of 8 V.

The results are shown in Table 5.

TABLE 5 Current (mA) Example 6 144 Example 7 520 Reference 14 Example 3

Referring to Table 5, the thin films of Examples 6 and 7 have moreexcellent electrical characteristics than that of Reference Example 3.

While this disclosure has been described in connection with what ispresently considered to be practical example embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments. On the contrary, it is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A light emitting device comprising a firstelectrode, a second electrode, a quantum dot layer disposed between thefirst electrode and the second electrode, and a first auxiliary layerdisposed between the quantum dot layer and the first electrode whereinthe first auxiliary layer comprises nickel oxide nanoparticles having anaverage particle diameter of less than or equal to about 10 nanometersand an organic ligand.
 2. The light emitting device of claim 1, whereinthe average particle diameter of the nickel oxide nanoparticles is lessthan about 5 nanometers.
 3. The light emitting device of claim 1,wherein about 90% or greater of a total number of the nickel oxidenanoparticles in the first auxiliary layer have a particle size within±about 30% of the average particle diameter of the nickel oxidenanoparticles.
 4. The light emitting device of claim 1, wherein thenickel oxide nanoparticles comprise a metal dopant other than nickel. 5.The light emitting device of claim 4, wherein the metal dopant comprisescopper, aluminum, molybdenum, vanadium, iron, lithium, manganese,silver, cobalt, zirconium, chromium, zinc, or a combination thereof. 6.The light emitting device of claim 4, wherein the metal dopant ispresent in an amount of less than or equal to about 20 weight percent,based on a total weight of the nickel oxide nanoparticles.
 7. The lightemitting device of claim 1, wherein the organic ligand is derived from asubstituted or unsubstituted C1 to C10 alkylamine compound, asubstituted or unsubstituted C2 to C10 carboxylic acid compound, or acombination thereof.
 8. The light emitting device of claim 1, whereinthe organic ligand is derived from a substituted or unsubstitutedpentylamine, a substituted or unsubstituted hexylamine, a substituted orunsubstituted heptylamine, a substituted or unsubstituted octylamine, asubstituted or unsubstituted nonylamine, a substituted or unsubstitutedpentanoic acid, a substituted or unsubstituted hexanoic acid, asubstituted or unsubstituted heptanoic acid, a substituted orunsubstituted octanoic acid, a substituted or unsubstituted nonanoicacid, or a combination thereof.
 9. The light emitting device of claim 1,wherein the organic ligand is present in an amount of less than or equalto about 30 weight percent, based on a total weight of the firstauxiliary layer.
 10. The light emitting device of claim 1, wherein thelight emitting device further comprises a second auxiliary layerdisposed between the first auxiliary layer and the quantum dot layer.11. The light emitting device of claim 10, wherein the second auxiliarylayer comprisespoly(9,9-dioctyl-fluorene-co-N-(4-butylphenyl)-diphenylamine,polyarylamine, poly(N-vinylcarbazole), poly(3,4-ethylenedioxythiophene),poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, polyaniline,polypyrrole, N,N,N′,N′-tetrakis (4-methoxyphenyl)-benzidine,4-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl,4,4′,4″-tris[phenyl(m-tolyl)amino]triphenylamine,4,4′,4″-tris(N-carbazolyl)-triphenylamine,1,1-bis[(di-4-tolylamino)phenylcyclohexane, a p-type metal oxide,graphene oxide, or a combination thereof.
 12. The light emitting deviceof claim 1, wherein the light emitting device further comprises a thirdauxiliary layer disposed between the quantum dot layer, and the secondelectrode and the third auxiliary layer comprise zinc oxidenanoparticles represented by Zn_(1-x)M_(x)O, wherein M is Mg, Ca, Zr, W,Li, Ti, or a combination thereof and 0≤x<0.5.
 13. The light emittingdevice of claim 1, which comprises an anode and a cathode, a lightemitting layer comprising a non-cadmium-based quantum dot disposedbetween the anode and the cathode, and a hole auxiliary layer disposedbetween the anode and the light emitting layer, the hole auxiliary layercomprising nickel oxide nanoparticles.
 14. A method of manufacturing alight emitting device, comprising providing a first electrode, forming afirst auxiliary layer comprising nickel oxide nanoparticles having anaverage particle diameter of less than or equal to about 10 nanometersand an organic ligand on the first electrode, forming a quantum dotlayer on the first auxiliary layer, and forming a second electrode onthe quantum dot layer to manufacture the light emitting device.
 15. Themethod of claim 14, wherein the forming of the first auxiliary layer isperformed by a solution process.
 16. The method of claim 14, wherein theforming of the first auxiliary layer comprises obtaining the nickeloxide nanoparticles and the organic ligand from a precursor mixturecomprising a nickel oxide precursor and an organic ligand precursor,obtaining a composition for a first auxiliary layer comprising thenickel oxide nanoparticles and the organic ligand, and coating thecomposition for the first auxiliary layer to form the first auxiliarylayer.
 17. The method of claim 16, wherein the organic ligand precursorcomprises a substituted or unsubstituted C1 to C10 alkylamine compound,a substituted or unsubstituted C2 to C10 carboxylic acid compound, or acombination thereof.
 18. The method of claim 16, wherein the organicligand precursor comprises a substituted or unsubstituted pentylamine, asubstituted or unsubstituted hexylamine, a substituted or unsubstitutedheptylamine, a substituted or unsubstituted octylamine, a substituted orunsubstituted nonylamine, a substituted or unsubstituted pentanoic acid,a substituted or unsubstituted hexanoic acid, a substituted orunsubstituted heptanoic acid, a substituted or unsubstituted octanoicacid, a substituted or unsubstituted nonanoic acid, or a combinationthereof.
 19. The method of claim 16, wherein the obtaining the nickeloxide nanoparticles and the organic ligand comprises heat treating theprecursor mixture at a temperature of less than or equal to about 150°C.
 20. The method of claim 16, wherein the coating of the compositionfor the first auxiliary layer comprises coating the composition for thefirst auxiliary layer by a spin coating, a spray coating, a slitcoating, a dip coating, an inkjet printing, a nozzle printing, a doctorblade coating, or a combination thereof.
 21. The method of claim 16,wherein the coating of the composition for the first auxiliary layercomprises heat-treating at a temperature of less than 500° C.
 22. Adisplay device comprising the light emitting device of claim 1.